Polysubstituted butyric acids, esters and derivatives of the general formula ##STR1## are described in U.S. Pat. Nos. 4,224,052; 4,313,754 and 4,383,848.
The threo isomers of these compounds are disclosed as being non-selective vegetation control agents while the erythro/threo isomer mixtures are disclosed as postemergence herbicides having selectivity in certain crops such as corn, barley and wheat and as preemergence herbicides having selectivity in crops such as corn, cotton, soybeans, wheat and barley.
A method for the preparation of substituted-diaryl-cyanobutyrates by the condensation of ethyl cinnamates with benzyl cyanides has recently been reported by M. M. Al-Arab and A. M. Issa in J. Chem. Eng. Data 31, pp. 261-262 (1986).
While the references disclose post-emergence herbicidal activity in general for some of the compounds, they do not indicate that any would be useful selective herbicides for use in controlling undesirable vegetation in transplanted rice. Further, they do not indicate that in order to obtain selectivity for use in transplanted rice only certain specific substitution patterns for R.sub.2 and R.sub.3 in the general formula are effective.
It is an object of this invention to provide compounds which contain the specific substituents in both R.sub.2 and R.sub.3 which are required to obtain selectivity in rice. It is another object of this invention to provide a method for controlling undesirable vegetation selectively in the presence of rice utilizing these compounds.